1. Field of the Invention
The present invention relates to a transmission casing for a bicycle which hermetically seals a transmission body of a bicycle.
2. Description of Background Art
JP-A-2001-180565 discloses a transmission casing which includes an integrally coupled resin-made casing body 70 which is divided into three parts in the vehicle-width direction. A transmission body is hermetically sealed by the transmission casing.
Further, on the above-mentioned transmission casing, a crankshaft 101, a motor shaft 116 and an output shaft 47 are rotatably supported.
In the above-mentioned transmission casing, metal-made reinforcing members 105 which bear an inter-axis force working between the crankshaft 101 and the motor shaft 116 are integrally molded to the inside of the resin-made casing body 70 at the time of molding the casing.
However, in the transmission casing described in JP-A-2001-180565, the constitutional ratio of the resin and the reinforcing member which takes the strength and the rigidity of the whole transmission casing into consideration is not adopted. Thus, respective constitutions which may be optimum for the reduction of weight are not particularly considered. Further, with respect to a situation in which the transmission casing includes a large number of transmission shafts such as a derailleur shaft, a transmission shaft and the like in addition to the crankshaft, the motor shaft and the output shaft, it is necessary to integrally mold the metal-made reinforcing member over the whole transmission casing. Accordingly, as a matter of course, the weight of the transmission casing per se is increased and at the same time, the structure becomes complicated.